THREAD_POOL_QUEUE_SIZE

The size of the task queue. When there are at least the core number of
threads in the pool, tasks will be placed in the queue. If the queue is empty, more threads
may be created (up to the maximum pool size). If the queue is full and
all threads have been created, the task is rejected.

THREAD_POOL_ENABLED

By default, the ParallelExecutor service uses a thread pool. In
environments (such as Google Application Engine) where thread creation is not allowed, this can be set to
"false", and deferred logic will, instead, execute immediately.